Off road work vehicles in the agricultural, mining and construction fields, such as tractors, and the like, have traditionally operated with manual steering. Improvements in control system design and related position sensing technology, such as global positioning systems (GPS), including differential correction systems, as well as real time kinematic (RTK) satellite navigation have led to an increase in the use of automatic guidance control systems for these vehicles. The combination of improved navigation input signals precisely identifying vehicle position and speed with sophisticated on board vehicle electronic control systems allows for automatic guidance systems capable of steering the vehicle with a high degree of accuracy when traversing terrain.
To provide this control, the prior art teaches using satellite positioning information by an onboard vehicle navigation control system to accurately determine and control a vehicle's position while operating in a field. A preplanned route, based on information previously known about the terrain of the field, or a control system generated route may be used. The control methods are well known in the art, and may involve multiple position transmitters or receivers, with various signals used to derive vehicle location, elevation, direction of travel or heading, and speed.
The task of precision guidance of an agricultural vehicle involves not only accurately determining vehicle position in a field, but also defining an efficient array of paths to be followed by the vehicle that will, in conjunction with the swath of an element associated with the vehicle, create an overall swath pattern that efficiently and effectively covers the crop area of a field. The pattern must be located and oriented on the field, and the physical characteristics and limitations of the vehicle and coupled element must be identified and provided to the navigation system. Element or header width, location of the element or header with respect to the vehicle, and limitations on the vehicle and associated element movement, such as minimum turning radius, must also be considered. With this information it is possible to define a series of swath lines for the vehicle to travel in an attempt to cover all cultivatable portions of a field without unnecessary gaps or overlaps.
Calculating the series of paths needed to cover an area without substantial gaps or overlaps is relatively straightforward for straight paths on level terrain; however, not all fields can be covered in this manner. Many fields require the use of paths having a curvature that varies along at least some portion of its length, whether to follow irregularly shaped boundaries, avoid obstacles within the field, follow topographic contours of the ground, implement agronomic farming practices, or contour the ground for irrigation. Such conditions preclude a complete reliance on geometrically predefined paths, such as straight lines or constant radius curves. In addition, many fields include hills or valleys of sufficient slope to create errors in swath pattern calculations based on an assumption of flat terrain. These errors have been seen to cause gaps or overlaps between swaths in some cases.
Previous attempts to correct for errors due to slopes in the terrain use GPS data to determine the slope of the terrain and make swath line corrections as a vehicle traverses the swath. Reference in this regard Keller et al., U.S. Pat. No. 6,463,374 which discloses a method for compensating for a decrease in the effective length of a sprayer rig boom when the sprayer rig is operating on sloped terrain. Based on the disclosure, and particularly FIG. 8A of that patent, it appears that swath path corrections are based on the slope of the terrain at the presently driven swath path. In other words, the system makes corrections to a swath line as it is driven based on the slope of the terrain immediately behind the vehicle (because of computation delays as explained at column 10, lines 22-25). Thus the system is making adjustments to the vehicle course as it traverses the swath and basing those adjustments on the computed slope information associated with the terrain within the same swath.
Practical considerations limit the utility of the system and method of the Keller patent. For example, in an articulated work vehicle, such as a tractor coupled with an element, the articulated portions of the vehicle may not rigidly follow the front portion of the work vehicle creating slippage at the articulated joints of the vehicle and coupled element. This slippage may be due to anticipated conditions, such as turning the work vehicle, or due to unanticipated conditions, such dry or muddy terrain, variations in moisture in hilly terrain, sharpness of the element, tire wear, and other conditions under which the element is not rigidly aligned with the front of the vehicle. This is especially important to note for sloping terrain because of slippage of the element down the slope. The operator may need to manually steer the vehicle to achieve the desired swath line to compensate for slippage. Swath line corrections according to the method of this patent may be ineffective either because they may not be implemented quickly enough to align the articulated portion of the vehicle to the desired swath line, or they will have been overridden by the manual steering of the operator.
Finally, swath lines are typically depicted on a map available to the operator for use during operation. Because the method and system of the referenced patent adjusts and executes the swath path contemporaneously, the swath line is not available to be depicted on a map for the operator. For this reason, the swath line should generally be calculated prior to the time the vehicle engages the swath rather than as the vehicle engages the swath as done in the referenced patent. Thus, what is sought is an apparatus and method to generate swath lines and swath patterns that include swath corrections to compensate for variations in the slope of a field which overcomes at least one of the problems, shortcomings or disadvantages set forth above.